Ultrahigh Speed Micromachining

A new ultrahigh speed micro-spindle has been developed for micromachining that can be used at rotational speeds as high as 500,000 rpm. Since conventional ball bearings or fluid lubricated journal bearings cannot be used at speeds beyond 300,000 rpm for any extended period of time, the new spindle uses a set of journal and thrust foil bearings. The micro-spindle was integrated with a 3-axis micro-milling machine. Cutting experiments were performed on an aluminum alloy at speeds greater than 300,000 rpm using 50 and 300 micron end-mills. The increase in rotational speed to 450,000 rpm in micro-milling of aluminum alloy allowed an increase in feed rate to nearly 800 mm/min (the maximum feed rate available by the positioning stage), thus increasing the material removal rate by more than two orders of magnitude. The dimensional accuracy of several straight cuts made at different feed rates and depths of cut was measured. Theoretical models and research on machining of industrial ceramics have shown that high-speed machining allows for smaller depths of cut by each diamond grit, thus reducing the contact forces and resulting in a reduced possibility of detrimental chipping and subsurface machining damage. Therefore, micro-grinding was performed on dental ceramics to evaluate the feasibility ultrahigh speed machining. In these studies several ceramics used for preparation of dental restorations were cut with diamond tools. The propensity for generation of machining-related damage, such as surface and subsurface microcracks, were greatly reduced by machining at ultrahigh speeds and high feed rates. Micro-machining at such high speeds, and in combination with high feed rates, has never been achieved before.